A semiconductor module using a semiconductor device that performs a so-called switching function is used in power circuits in a wide field. In particular, a semiconductor module for use in, for example, power circuits of trains or of industrial equipment is required to have high withstand voltage, heavy electric current, and high heat dissipation ability. FIG. 28 shows one example of a conventional semiconductor module that is usable for such purposes (see Patent Literature 1, for example). The semiconductor module 900 shown in this figure has conductor layers 992 and 993 made of, for example, Cu on both sides of an insulating substrate 991 made of Al2O3. A semiconductor device 994 is bonded to the conductor layer 992 with a solder layer 995 therebetween. The semiconductor device 994 is arranged as, for example, an IGBT (Insulated Gate Bipolar Transistor). A heat dissipation plate 997 made of, for example, Cu is bonded to the conductor layer 993 with a solder layer 996 therebetween.
When the semiconductor module 900 is used for trains or for industrial equipment, the heat dissipation plate 997 is attached to a fixing board (not shown) mounted in these devices. However, when the semiconductor module 900 is produced, the heat dissipation plate 997 is liable to deform so that its upper side becomes convex in FIG. 28. As a result, a gap is made between the board and the heat dissipation plate 997. Therefore, it is impossible to appropriately dissipate heat from the semiconductor module 900. This hinders the enhancement of an electric current.